From ea3de9ce8aa280c5175c835bd3e94a3a9b814b74 Mon Sep 17 00:00:00 2001 From: Evan Green Date: Fri, 7 Apr 2023 16:10:59 -0700 Subject: RISC-V: Add a syscall for HW probing We don't have enough space for these all in ELF_HWCAP{,2} and there's no system call that quite does this, so let's just provide an arch-specific one to probe for hardware capabilities. This currently just provides m{arch,imp,vendor}id, but with the key-value pairs we can pass more in the future. Co-developed-by: Palmer Dabbelt Signed-off-by: Evan Green Reviewed-by: Conor Dooley Reviewed-by: Heiko Stuebner Tested-by: Heiko Stuebner Reviewed-by: Paul Walmsley Link: https://lore.kernel.org/r/20230407231103.2622178-3-evan@rivosinc.com Signed-off-by: Palmer Dabbelt --- Documentation/riscv/hwprobe.rst | 41 +++++++++++++++++++++++++++++++++++++++++ Documentation/riscv/index.rst | 1 + 2 files changed, 42 insertions(+) create mode 100644 Documentation/riscv/hwprobe.rst (limited to 'Documentation/riscv') diff --git a/Documentation/riscv/hwprobe.rst b/Documentation/riscv/hwprobe.rst new file mode 100644 index 000000000000..211828f706e3 --- /dev/null +++ b/Documentation/riscv/hwprobe.rst @@ -0,0 +1,41 @@ +.. SPDX-License-Identifier: GPL-2.0 + +RISC-V Hardware Probing Interface +--------------------------------- + +The RISC-V hardware probing interface is based around a single syscall, which +is defined in :: + + struct riscv_hwprobe { + __s64 key; + __u64 value; + }; + + long sys_riscv_hwprobe(struct riscv_hwprobe *pairs, size_t pair_count, + size_t cpu_count, cpu_set_t *cpus, + unsigned int flags); + +The arguments are split into three groups: an array of key-value pairs, a CPU +set, and some flags. The key-value pairs are supplied with a count. Userspace +must prepopulate the key field for each element, and the kernel will fill in the +value if the key is recognized. If a key is unknown to the kernel, its key field +will be cleared to -1, and its value set to 0. The CPU set is defined by +CPU_SET(3). For value-like keys (eg. vendor/arch/impl), the returned value will +be only be valid if all CPUs in the given set have the same value. Otherwise -1 +will be returned. For boolean-like keys, the value returned will be a logical +AND of the values for the specified CPUs. Usermode can supply NULL for cpus and +0 for cpu_count as a shortcut for all online CPUs. There are currently no flags, +this value must be zero for future compatibility. + +On success 0 is returned, on failure a negative error code is returned. + +The following keys are defined: + +* :c:macro:`RISCV_HWPROBE_KEY_MVENDORID`: Contains the value of ``mvendorid``, + as defined by the RISC-V privileged architecture specification. + +* :c:macro:`RISCV_HWPROBE_KEY_MARCHID`: Contains the value of ``marchid``, as + defined by the RISC-V privileged architecture specification. + +* :c:macro:`RISCV_HWPROBE_KEY_MIMPLID`: Contains the value of ``mimplid``, as + defined by the RISC-V privileged architecture specification. diff --git a/Documentation/riscv/index.rst b/Documentation/riscv/index.rst index 2e5b18fbb145..175a91db0200 100644 --- a/Documentation/riscv/index.rst +++ b/Documentation/riscv/index.rst @@ -7,6 +7,7 @@ RISC-V architecture boot-image-header vm-layout + hwprobe patch-acceptance uabi -- cgit v1.2.3 From 00e76e2c6a2bd3976d44d4a1fdd0b7a3c2566607 Mon Sep 17 00:00:00 2001 From: Evan Green Date: Fri, 7 Apr 2023 16:11:00 -0700 Subject: RISC-V: hwprobe: Add support for RISCV_HWPROBE_BASE_BEHAVIOR_IMA We have an implicit set of base behaviors that userspace depends on, which are mostly defined in various ISA specifications. Co-developed-by: Palmer Dabbelt Signed-off-by: Evan Green Reviewed-by: Conor Dooley Reviewed-by: Heiko Stuebner Tested-by: Heiko Stuebner Reviewed-by: Paul Walmsley Link: https://lore.kernel.org/r/20230407231103.2622178-4-evan@rivosinc.com Signed-off-by: Palmer Dabbelt --- Documentation/riscv/hwprobe.rst | 24 ++++++++++++++++++++++++ arch/riscv/include/asm/hwprobe.h | 2 +- arch/riscv/include/uapi/asm/hwprobe.h | 5 +++++ arch/riscv/kernel/sys_riscv.c | 20 ++++++++++++++++++++ 4 files changed, 50 insertions(+), 1 deletion(-) (limited to 'Documentation/riscv') diff --git a/Documentation/riscv/hwprobe.rst b/Documentation/riscv/hwprobe.rst index 211828f706e3..945d44683c40 100644 --- a/Documentation/riscv/hwprobe.rst +++ b/Documentation/riscv/hwprobe.rst @@ -39,3 +39,27 @@ The following keys are defined: * :c:macro:`RISCV_HWPROBE_KEY_MIMPLID`: Contains the value of ``mimplid``, as defined by the RISC-V privileged architecture specification. + +* :c:macro:`RISCV_HWPROBE_KEY_BASE_BEHAVIOR`: A bitmask containing the base + user-visible behavior that this kernel supports. The following base user ABIs + are defined: + + * :c:macro:`RISCV_HWPROBE_BASE_BEHAVIOR_IMA`: Support for rv32ima or + rv64ima, as defined by version 2.2 of the user ISA and version 1.10 of the + privileged ISA, with the following known exceptions (more exceptions may be + added, but only if it can be demonstrated that the user ABI is not broken): + + * The :fence.i: instruction cannot be directly executed by userspace + programs (it may still be executed in userspace via a + kernel-controlled mechanism such as the vDSO). + +* :c:macro:`RISCV_HWPROBE_KEY_IMA_EXT_0`: A bitmask containing the extensions + that are compatible with the :c:macro:`RISCV_HWPROBE_BASE_BEHAVIOR_IMA`: + base system behavior. + + * :c:macro:`RISCV_HWPROBE_IMA_FD`: The F and D extensions are supported, as + defined by commit cd20cee ("FMIN/FMAX now implement + minimumNumber/maximumNumber, not minNum/maxNum") of the RISC-V ISA manual. + + * :c:macro:`RISCV_HWPROBE_IMA_C`: The C extension is supported, as defined + by version 2.2 of the RISC-V ISA manual. diff --git a/arch/riscv/include/asm/hwprobe.h b/arch/riscv/include/asm/hwprobe.h index 6184bbc77256..d717c80a64ff 100644 --- a/arch/riscv/include/asm/hwprobe.h +++ b/arch/riscv/include/asm/hwprobe.h @@ -8,6 +8,6 @@ #include -#define RISCV_HWPROBE_MAX_KEY 2 +#define RISCV_HWPROBE_MAX_KEY 4 #endif diff --git a/arch/riscv/include/uapi/asm/hwprobe.h b/arch/riscv/include/uapi/asm/hwprobe.h index b79be00920db..398e08f7e083 100644 --- a/arch/riscv/include/uapi/asm/hwprobe.h +++ b/arch/riscv/include/uapi/asm/hwprobe.h @@ -20,6 +20,11 @@ struct riscv_hwprobe { #define RISCV_HWPROBE_KEY_MVENDORID 0 #define RISCV_HWPROBE_KEY_MARCHID 1 #define RISCV_HWPROBE_KEY_MIMPID 2 +#define RISCV_HWPROBE_KEY_BASE_BEHAVIOR 3 +#define RISCV_HWPROBE_BASE_BEHAVIOR_IMA (1 << 0) +#define RISCV_HWPROBE_KEY_IMA_EXT_0 4 +#define RISCV_HWPROBE_IMA_FD (1 << 0) +#define RISCV_HWPROBE_IMA_C (1 << 1) /* Increase RISCV_HWPROBE_MAX_KEY when adding items. */ #endif diff --git a/arch/riscv/kernel/sys_riscv.c b/arch/riscv/kernel/sys_riscv.c index fe8e833ecb2e..5ca567cef142 100644 --- a/arch/riscv/kernel/sys_riscv.c +++ b/arch/riscv/kernel/sys_riscv.c @@ -9,6 +9,7 @@ #include #include #include +#include #include #include #include @@ -125,6 +126,25 @@ static void hwprobe_one_pair(struct riscv_hwprobe *pair, case RISCV_HWPROBE_KEY_MIMPID: hwprobe_arch_id(pair, cpus); break; + /* + * The kernel already assumes that the base single-letter ISA + * extensions are supported on all harts, and only supports the + * IMA base, so just cheat a bit here and tell that to + * userspace. + */ + case RISCV_HWPROBE_KEY_BASE_BEHAVIOR: + pair->value = RISCV_HWPROBE_BASE_BEHAVIOR_IMA; + break; + + case RISCV_HWPROBE_KEY_IMA_EXT_0: + pair->value = 0; + if (has_fpu()) + pair->value |= RISCV_HWPROBE_IMA_FD; + + if (riscv_isa_extension_available(NULL, c)) + pair->value |= RISCV_HWPROBE_IMA_C; + + break; /* * For forward compatibility, unknown keys don't fail the whole -- cgit v1.2.3 From 62a31d6e38bd0faef7c956b358d651f7bdc4ae0c Mon Sep 17 00:00:00 2001 From: Evan Green Date: Fri, 7 Apr 2023 16:11:01 -0700 Subject: RISC-V: hwprobe: Support probing of misaligned access performance This allows userspace to select various routines to use based on the performance of misaligned access on the target hardware. Rather than adding DT bindings, this change taps into the alternatives mechanism used to probe CPU errata. Add a new function pointer alongside the vendor-specific errata_patch_func() that probes for desirable errata (otherwise known as "features"). Unlike the errata_patch_func(), this function is called on each CPU as it comes up, so it can save feature information per-CPU. The T-head C906 has fast unaligned access, both as defined by GCC [1], and in performing a basic benchmark, which determined that byte copies are >50% slower than a misaligned word copy of the same data size (source for this test at [2]): bytecopy size f000 count 50000 offset 0 took 31664899 us wordcopy size f000 count 50000 offset 0 took 5180919 us wordcopy size f000 count 50000 offset 1 took 13416949 us [1] https://github.com/gcc-mirror/gcc/blob/master/gcc/config/riscv/riscv.cc#L353 [2] https://pastebin.com/EPXvDHSW Co-developed-by: Palmer Dabbelt Signed-off-by: Evan Green Reviewed-by: Heiko Stuebner Tested-by: Heiko Stuebner Reviewed-by: Conor Dooley Reviewed-by: Paul Walmsley Link: https://lore.kernel.org/r/20230407231103.2622178-5-evan@rivosinc.com Signed-off-by: Palmer Dabbelt --- Documentation/riscv/hwprobe.rst | 21 +++++++++++++++++++++ arch/riscv/errata/thead/errata.c | 10 ++++++++++ arch/riscv/include/asm/alternative.h | 5 +++++ arch/riscv/include/asm/cpufeature.h | 2 ++ arch/riscv/include/asm/hwprobe.h | 2 +- arch/riscv/include/uapi/asm/hwprobe.h | 7 +++++++ arch/riscv/kernel/alternative.c | 19 +++++++++++++++++++ arch/riscv/kernel/cpufeature.c | 3 +++ arch/riscv/kernel/smpboot.c | 1 + arch/riscv/kernel/sys_riscv.c | 28 ++++++++++++++++++++++++++++ 10 files changed, 97 insertions(+), 1 deletion(-) (limited to 'Documentation/riscv') diff --git a/Documentation/riscv/hwprobe.rst b/Documentation/riscv/hwprobe.rst index 945d44683c40..9f0dd62dcb5d 100644 --- a/Documentation/riscv/hwprobe.rst +++ b/Documentation/riscv/hwprobe.rst @@ -63,3 +63,24 @@ The following keys are defined: * :c:macro:`RISCV_HWPROBE_IMA_C`: The C extension is supported, as defined by version 2.2 of the RISC-V ISA manual. + +* :c:macro:`RISCV_HWPROBE_KEY_CPUPERF_0`: A bitmask that contains performance + information about the selected set of processors. + + * :c:macro:`RISCV_HWPROBE_MISALIGNED_UNKNOWN`: The performance of misaligned + accesses is unknown. + + * :c:macro:`RISCV_HWPROBE_MISALIGNED_EMULATED`: Misaligned accesses are + emulated via software, either in or below the kernel. These accesses are + always extremely slow. + + * :c:macro:`RISCV_HWPROBE_MISALIGNED_SLOW`: Misaligned accesses are supported + in hardware, but are slower than the cooresponding aligned accesses + sequences. + + * :c:macro:`RISCV_HWPROBE_MISALIGNED_FAST`: Misaligned accesses are supported + in hardware and are faster than the cooresponding aligned accesses + sequences. + + * :c:macro:`RISCV_HWPROBE_MISALIGNED_UNSUPPORTED`: Misaligned accesses are + not supported at all and will generate a misaligned address fault. diff --git a/arch/riscv/errata/thead/errata.c b/arch/riscv/errata/thead/errata.c index 3b96a06d3c54..5b6d62586a8b 100644 --- a/arch/riscv/errata/thead/errata.c +++ b/arch/riscv/errata/thead/errata.c @@ -11,7 +11,9 @@ #include #include #include +#include #include +#include #include #include @@ -115,3 +117,11 @@ void __init_or_module thead_errata_patch_func(struct alt_entry *begin, struct al if (stage == RISCV_ALTERNATIVES_EARLY_BOOT) local_flush_icache_all(); } + +void __init_or_module thead_feature_probe_func(unsigned int cpu, + unsigned long archid, + unsigned long impid) +{ + if ((archid == 0) && (impid == 0)) + per_cpu(misaligned_access_speed, cpu) = RISCV_HWPROBE_MISALIGNED_FAST; +} diff --git a/arch/riscv/include/asm/alternative.h b/arch/riscv/include/asm/alternative.h index b8648d4f2ac1..b5774e24d4a3 100644 --- a/arch/riscv/include/asm/alternative.h +++ b/arch/riscv/include/asm/alternative.h @@ -28,6 +28,7 @@ #define ALT_OLD_PTR(a) __ALT_PTR(a, old_offset) #define ALT_ALT_PTR(a) __ALT_PTR(a, alt_offset) +void __init probe_vendor_features(unsigned int cpu); void __init apply_boot_alternatives(void); void __init apply_early_boot_alternatives(void); void apply_module_alternatives(void *start, size_t length); @@ -55,11 +56,15 @@ void thead_errata_patch_func(struct alt_entry *begin, struct alt_entry *end, unsigned long archid, unsigned long impid, unsigned int stage); +void thead_feature_probe_func(unsigned int cpu, unsigned long archid, + unsigned long impid); + void riscv_cpufeature_patch_func(struct alt_entry *begin, struct alt_entry *end, unsigned int stage); #else /* CONFIG_RISCV_ALTERNATIVE */ +static inline void probe_vendor_features(unsigned int cpu) { } static inline void apply_boot_alternatives(void) { } static inline void apply_early_boot_alternatives(void) { } static inline void apply_module_alternatives(void *start, size_t length) { } diff --git a/arch/riscv/include/asm/cpufeature.h b/arch/riscv/include/asm/cpufeature.h index 66ebaae449c8..808d5403f2ac 100644 --- a/arch/riscv/include/asm/cpufeature.h +++ b/arch/riscv/include/asm/cpufeature.h @@ -18,4 +18,6 @@ struct riscv_cpuinfo { DECLARE_PER_CPU(struct riscv_cpuinfo, riscv_cpuinfo); +DECLARE_PER_CPU(long, misaligned_access_speed); + #endif diff --git a/arch/riscv/include/asm/hwprobe.h b/arch/riscv/include/asm/hwprobe.h index d717c80a64ff..78936f4ff513 100644 --- a/arch/riscv/include/asm/hwprobe.h +++ b/arch/riscv/include/asm/hwprobe.h @@ -8,6 +8,6 @@ #include -#define RISCV_HWPROBE_MAX_KEY 4 +#define RISCV_HWPROBE_MAX_KEY 5 #endif diff --git a/arch/riscv/include/uapi/asm/hwprobe.h b/arch/riscv/include/uapi/asm/hwprobe.h index 398e08f7e083..8d745a4ad8a2 100644 --- a/arch/riscv/include/uapi/asm/hwprobe.h +++ b/arch/riscv/include/uapi/asm/hwprobe.h @@ -25,6 +25,13 @@ struct riscv_hwprobe { #define RISCV_HWPROBE_KEY_IMA_EXT_0 4 #define RISCV_HWPROBE_IMA_FD (1 << 0) #define RISCV_HWPROBE_IMA_C (1 << 1) +#define RISCV_HWPROBE_KEY_CPUPERF_0 5 +#define RISCV_HWPROBE_MISALIGNED_UNKNOWN (0 << 0) +#define RISCV_HWPROBE_MISALIGNED_EMULATED (1 << 0) +#define RISCV_HWPROBE_MISALIGNED_SLOW (2 << 0) +#define RISCV_HWPROBE_MISALIGNED_FAST (3 << 0) +#define RISCV_HWPROBE_MISALIGNED_UNSUPPORTED (4 << 0) +#define RISCV_HWPROBE_MISALIGNED_MASK (7 << 0) /* Increase RISCV_HWPROBE_MAX_KEY when adding items. */ #endif diff --git a/arch/riscv/kernel/alternative.c b/arch/riscv/kernel/alternative.c index 2354c69dc7d1..fc65c9293ac5 100644 --- a/arch/riscv/kernel/alternative.c +++ b/arch/riscv/kernel/alternative.c @@ -27,6 +27,8 @@ struct cpu_manufacturer_info_t { void (*patch_func)(struct alt_entry *begin, struct alt_entry *end, unsigned long archid, unsigned long impid, unsigned int stage); + void (*feature_probe_func)(unsigned int cpu, unsigned long archid, + unsigned long impid); }; static void __init_or_module riscv_fill_cpu_mfr_info(struct cpu_manufacturer_info_t *cpu_mfr_info) @@ -41,6 +43,7 @@ static void __init_or_module riscv_fill_cpu_mfr_info(struct cpu_manufacturer_inf cpu_mfr_info->imp_id = sbi_get_mimpid(); #endif + cpu_mfr_info->feature_probe_func = NULL; switch (cpu_mfr_info->vendor_id) { #ifdef CONFIG_ERRATA_SIFIVE case SIFIVE_VENDOR_ID: @@ -50,6 +53,7 @@ static void __init_or_module riscv_fill_cpu_mfr_info(struct cpu_manufacturer_inf #ifdef CONFIG_ERRATA_THEAD case THEAD_VENDOR_ID: cpu_mfr_info->patch_func = thead_errata_patch_func; + cpu_mfr_info->feature_probe_func = thead_feature_probe_func; break; #endif default: @@ -139,6 +143,20 @@ void riscv_alternative_fix_offsets(void *alt_ptr, unsigned int len, } } +/* Called on each CPU as it starts */ +void __init_or_module probe_vendor_features(unsigned int cpu) +{ + struct cpu_manufacturer_info_t cpu_mfr_info; + + riscv_fill_cpu_mfr_info(&cpu_mfr_info); + if (!cpu_mfr_info.feature_probe_func) + return; + + cpu_mfr_info.feature_probe_func(cpu, + cpu_mfr_info.arch_id, + cpu_mfr_info.imp_id); +} + /* * This is called very early in the boot process (directly after we run * a feature detect on the boot CPU). No need to worry about other CPUs @@ -193,6 +211,7 @@ void __init apply_boot_alternatives(void) /* If called on non-boot cpu things could go wrong */ WARN_ON(smp_processor_id() != 0); + probe_vendor_features(0); _apply_alternatives((struct alt_entry *)__alt_start, (struct alt_entry *)__alt_end, RISCV_ALTERNATIVES_BOOT); diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c index 59d58ee0f68d..8bbc89351050 100644 --- a/arch/riscv/kernel/cpufeature.c +++ b/arch/riscv/kernel/cpufeature.c @@ -30,6 +30,9 @@ unsigned long elf_hwcap __read_mostly; /* Host ISA bitmap */ static DECLARE_BITMAP(riscv_isa, RISCV_ISA_EXT_MAX) __read_mostly; +/* Performance information */ +DEFINE_PER_CPU(long, misaligned_access_speed); + /** * riscv_isa_extension_base() - Get base extension word * diff --git a/arch/riscv/kernel/smpboot.c b/arch/riscv/kernel/smpboot.c index ddb2afba6d25..2867c12c3d16 100644 --- a/arch/riscv/kernel/smpboot.c +++ b/arch/riscv/kernel/smpboot.c @@ -168,6 +168,7 @@ asmlinkage __visible void smp_callin(void) notify_cpu_starting(curr_cpuid); numa_add_cpu(curr_cpuid); set_cpu_online(curr_cpuid, 1); + probe_vendor_features(curr_cpuid); /* * Remote TLB flushes are ignored while the CPU is offline, so emit diff --git a/arch/riscv/kernel/sys_riscv.c b/arch/riscv/kernel/sys_riscv.c index 5ca567cef142..55389e7595f6 100644 --- a/arch/riscv/kernel/sys_riscv.c +++ b/arch/riscv/kernel/sys_riscv.c @@ -7,6 +7,7 @@ #include #include +#include #include #include #include @@ -117,6 +118,29 @@ static void hwprobe_arch_id(struct riscv_hwprobe *pair, pair->value = id; } +static u64 hwprobe_misaligned(const struct cpumask *cpus) +{ + int cpu; + u64 perf = -1ULL; + + for_each_cpu(cpu, cpus) { + int this_perf = per_cpu(misaligned_access_speed, cpu); + + if (perf == -1ULL) + perf = this_perf; + + if (perf != this_perf) { + perf = RISCV_HWPROBE_MISALIGNED_UNKNOWN; + break; + } + } + + if (perf == -1ULL) + return RISCV_HWPROBE_MISALIGNED_UNKNOWN; + + return perf; +} + static void hwprobe_one_pair(struct riscv_hwprobe *pair, const struct cpumask *cpus) { @@ -146,6 +170,10 @@ static void hwprobe_one_pair(struct riscv_hwprobe *pair, break; + case RISCV_HWPROBE_KEY_CPUPERF_0: + pair->value = hwprobe_misaligned(cpus); + break; + /* * For forward compatibility, unknown keys don't fail the whole * call, but get their element key set to -1 and value set to 0 -- cgit v1.2.3